A filter core in a purifier has a limited service life. The filter core has to be replaced in time when the filter core is stuck with dirt, to ensure the air purifying effect.
In a related art, when the purifier is operated at various levels of power, in order to calculate a current consumed lifespan, a service time period at each level of power is recorded, the recorded service time periods are respectively multiplied with corresponding coefficients, and the products are sum up as the current consumed lifespan.